import {synchronizeProducts} from 'app/gen-server/entity/Product';
import {Mutex} from 'async-mutex';
import {Connection, createConnection, getConnection} from 'typeorm';

// Summary of migrations found in database and in code.
interface MigrationSummary {
  migrationsInDb: string[];
  migrationsInCode: string[];
  pendingMigrations: string[];
}

// Find the migrations in the database, the migrations in the codebase, and compare the two.
export async function getMigrations(connection: Connection): Promise<MigrationSummary> {
  let migrationsInDb: string[];
  try {
    migrationsInDb = (await connection.query('select name from migrations')).map((rec: any) => rec.name);
  } catch (e) {
    // If no migrations have run, there'll be no migrations table - which is fine,
    // it just means 0 migrations run yet.  Sqlite+Postgres report this differently,
    // so any query error that mentions the name of our table is treated as ok.
    // Everything else is unexpected.
    if (!(e.name === 'QueryFailedError' && e.message.includes('migrations'))) {
      throw e;
    }
    migrationsInDb = [];
  }
  // get the migration names in codebase.
  // They are a bit hidden, see typeorm/src/migration/MigrationExecutor::getMigrations
  const migrationsInCode: string[] = connection.migrations.map(m => (m.constructor as any).name);
  const pendingMigrations = migrationsInCode.filter(m => !migrationsInDb.includes(m));
  return {
    migrationsInDb,
    migrationsInCode,
    pendingMigrations,
  };
}

/**
 * Run any needed migrations, and make sure products are up to date.
 */
export async function updateDb(connection?: Connection) {
  connection = connection || await getOrCreateConnection();
  await runMigrations(connection);
  await synchronizeProducts(connection, true);
}

/**
 * Get a connection to db if one exists, or create one. Serialized to
 * avoid duplication.
 */
const connectionMutex = new Mutex();
export async function getOrCreateConnection(): Promise<Connection> {
  return connectionMutex.runExclusive(async() => {
    try {
      // If multiple servers are started within the same process, we
      // share the database connection.  This saves locking trouble
      // with Sqlite.
      return getConnection();
    } catch (e) {
      const connection = await createConnection();
      // When using Sqlite, set a busy timeout of 3s to tolerate a little
      // interference from connections made by tests. Logging doesn't show
      // any particularly slow queries, but bad luck is possible.
      // This doesn't affect when Postgres is in use. It also doesn't have
      // any impact when there is a single connection to the db, as is the
      // case when Grist is run as a single process.
      if (connection.driver.options.type === 'sqlite') {
        await connection.query('PRAGMA busy_timeout = 3000');
      }
      return connection;
    }
  });
}

export async function runMigrations(connection: Connection) {
  // on SQLite, migrations fail if we don't temporarily disable foreign key
  // constraint checking.  This is because for sqlite typeorm copies each
  // table and rebuilds it from scratch for each schema change.
  // Also, we need to disable foreign key constraint checking outside of any
  // transaction, or it has no effect.
  const sqlite = connection.driver.options.type === 'sqlite';
  if (sqlite) { await connection.query("PRAGMA foreign_keys = OFF;"); }
  await connection.transaction(async tr => {
    await tr.connection.runMigrations();
  });
  if (sqlite) { await connection.query("PRAGMA foreign_keys = ON;"); }
}

export async function undoLastMigration(connection: Connection) {
  const sqlite = connection.driver.options.type === 'sqlite';
  if (sqlite) { await connection.query("PRAGMA foreign_keys = OFF;"); }
  await connection.transaction(async tr => {
    await tr.connection.undoLastMigration();
  });
  if (sqlite) { await connection.query("PRAGMA foreign_keys = ON;"); }
}